Solar tracking

tbrooks tbrooks at
Thu Jan 27 12:46:01 EST 2000

I'm sorry Henrik, you are mistaken - growth has nothing to do with the
process.  Please review the following references:

Taiz L,  and Zeigler E (1991). Plant Physiology. The Benjamin/Cummings
Publishing Co., Inc.  Redwood City, CA, USA.  p. 253.:

Alfalfa, cotton, legumes including soybean and bean, and some wild species
of the Malvaceae are examples of the numerous species capable of solar
tracking.  In many cases, leaf orientation is controlled by a specialized
organ called the pulvinus, found at the junction between the blade and the
petiole.  The pulvinus has motor cells that change their osmotic potential
and generate mechanical forces that cause the blade dispacement.  In other
plants, leaf orientation is controlled by small mechanical changes along the
length of the petiole and by movements of the younger parts of the stem.
Both phytochrome and a blue light sensitive pigment have been implicated as
photoreceptors in solar tracking.

Nobel PS (1991).  Physiochemicals and Environmental Plant Physiology.
Academic Press Inc., NY, USA. p. 384.

The mechanism for solar tracking invloves changes in hydrostatic pressure
induced by the absoption of blue light by photoreceptors in the leaf veins
or the pulvinus, perhaps via steps similar to those for stomatal opening
discussed in the next champter, leading to changes in leaf orientation.


Koller D (1986).  Yearly Review: The control of leaf orientation by light.
Photochemistry and Photobiology.  44: 819-826.

Regarding cotton - it is an amazing thing to watch - you can watch the
leaves turning throughout the day!


Talbot J. Brooks
Dept. of Plant Biology
Arizona State University
Tempe, AZ


US Water Conservation Laboratory
US Dept. Of Agriculture, Agricultural Research Service
4331 E Broadway
Phoenix, AZ 85040

----- Original Message -----
From: "Buschmann, Henrik" <buschmann at>
To: <tbrooks at>; <patrickhall at>; "Buschmann,
Henrik" <buschmann at>; <plantbio at>
Sent: Thursday, January 27, 2000 10:18 AM
Subject: AW: Solar tracking

> Hallo Talbot,
> i dont agree totaly: concerning the flux of water i believe it is better
> call these events growth (as a generalization). The receptor should be
> cryptochrome (at least when blue light is the signal).
> Anyhows, what your saying about cotton (in contrast to sunflower) sounds
> interesting to me. Do you know any literature concerning cotton (and solar
> track.)?
> Cheers,
> Henrik
> -----Ursprüngliche Nachricht-----
> Von: tbrooks [mailto:tbrooks at]
> Gesendet am: Montag, 24. Januar 2000 14:17
> An: patrickhall at; buschmann at
> Betreff: Solar tracking
>     Solar tracking, or heliotropism, is a phytochrome mediated response..
> Phytochrome is a pigment sensitive to blue light.  Basically what happens
> blue light falls on phytochrome which induces a signal transduction
> of ion exchanges, most often in stem tissue.  The end result of this
> transduction is the movement of water into tissues (again, most often the
> stems areas), elongating or stiffening a portion such that the desired
> now faces the sun.  For example, at sunrise, the tissue on the west side
> the stem would become more rigid and point a leaf to the east.  As the sun
> moves, the relative amount of "signal" being transmitted by phytochrome
> moderates accordingly, allowing the organ (a leaf or flower) to track the
> sun.  I do not know the number of plants out there that do this, but some
> great examples are sunflower (flowers track) and cotton (leaves track).  I
> can't post to the group from my server, but thought you might find this
> interesting none the less..
> Regards,
> Talbot J. Brooks
> Graduate Student Researcher
> 4331 E. Broadway Rd..
> Phoenix, AZ 85040
> Office: (602) 379-4356 ext. 262
> Fax:    (602) 379-4355
> tbrooks at <mailto:tbrooks at>
> Visit our web site at:
> <>


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